Flash memory, or memory which can be electronically erased and reprogrammed, is also known as EEPROM. Flash memory, which unlike ordinary RAM, does not lose the stored information upon a power off condition. Many products or designs maintain objects, and their revisions, including program code, login data, operating parameters, usage settings, and firmware, in flash memory, to allow these objects to be changed during use, but retained after loss of power. Flash memory is typically used in PC BIOS initialization operations. Most products that embed such objects offer facilities for replacing or modifying their contents. For example, the operating firmware for a given device, such as a magnetic disk, may be updated.
A problem arises during a flash update, in that the update process may not complete. Thus, the updated revision may be incomplete, and unusable. If the system only maintains a single copy in a single allocated storage area, meaning that no prior versions exist, then the system can suffer loss of state if an error occurs while the object is being replaced.
A prior art alternative to the single copy mechanism is to maintain prior versions of the object. However, updating these objects can cause multiple revisions of objects to be present, and thus requires a mechanism to determine which object is valid and should be used. Typically, a version is considered valid if it is the most recent, complete version. The second mechanism has a larger storage area, in which multiple revisions of the object may be maintained, where only one is active, usually the valid version. The prior art assigns each version a tag which is incremented via a counter after each assignment. During initialization of the system, a software algorithm examines the tags, and thus determines which object to activate.
However, such implementations that store multiple revisions using a finite revision tags have problems when the revision tag reaches its maximal value. The next tag value is then the lowest tag, and thus, the most recent version is tagged with the lowest value tag, and since applications assume that the highest tag value represents the most recent version, the most recent version will not be used during system operations. This is known as rollover effects. Note that the tags are represented by a fixed field, and the tag is usually an index or revision number, or a date code. These tag fields are limited in that they have an inherent maximum value, due to the physical size of the storage allocated for maintaining the tag field. The consequence of this bounded tags and rollover effects is that revision management algorithms may generate indeterminate, and hence incorrect, results.
Therefore, there is a need in the art for a mechanism that will allow multiple versions of objects to be stored in a non-volatile memory without the rollover limitations of bounded tags.